1. Field of the Invention
The present invention relates to multiple-beam antennas. More specifically, the present invention relates to a multiple-beam antenna provided with a low noise down converter receiving signals from a plurality of communications satellites for amplification and frequency conversion, and outputting the signals to a tuner circuit.
2. Description of the Background Art
In satellite broadcasting or satellite communication, a radio wave output from a satellite is transmitted in the form of a circularly polarized wave or linearly polarized wave. The radio wave is converted to mutually orthogonal horizontally and vertically polarized-waves by a low noise down converter and input to a tuner circuit.
In satellite broadcasting, a circularly polarized wave is employed as there is no need to consider polarization displacement resulting from a geometrical relationship with respect to a receiving point on the earth. In satellite communication, however, a linearly polarized wave is employed which is orthogonal to vertically and horizontally polarized waves.
FIG. 5 is an illustration showing a conventional parabolic antenna receiving a radio wave output from a satellite. The radio wave output from the satellite and having vertical and horizontal planes of polarization is reflected by parabolic antenna 1 and input to a down converter 2. Down converter 2 includes a circular waveguide 3 as shown in FIG. 6. The radio wave is input to an opening of circular waveguide 3, converted to a linearly polarized wave, and fed to a circuit board (not shown). A reflecting bar 4 is provided inside circular waveguide 3 shown in FIG. 6, and probes 5 and 6 are also inserted to circular waveguide 3. The vertically polarized wave is reflected by reflecting bar 4 and output to probe 6, whereas the horizontally polarized wave is directly output to probe 5.
In adjusting polarization displacement using circular waveguide 3 shown in FIG. 6, feeding probes 5, 6 and circular waveguide 3 are orthogonally arranged. The polarization displacement is adjusted by rotating down converter 2 which is integrally formed with waveguide 3, as shown in FIG. 7, when mounting down converter 2 to parabolic antenna 1.
FIG. 8 is a diagram shown in conjunction with a multiple-beam antenna. Referring to FIG. 8, radio waves transmitted from two satellites 10 and 11 are reflected by parabolic reflector 8 and received by one low noise block down converter (hereinafter abbreviated as LNB) 9, which is supported by parabolic reflector 81 through a supporting arm 82. The received signals from two satellites are switched by a signal selected by a tuner. Each of the radio waves transmitted from two satellites has a different focal point, so that a waveguide is provided at the input portion for each satellite in LNB 9 for separation of radio waves.
FIG. 9 shows a multiple-beam LNB integrally formed with the waveguide. As shown in FIG. 8, an entire system allowing reception of the radio waves from a plurality of satellites 10, 11 by one LNB 9 is referred to as a multiple-beam antenna. Particularly, the waveguide of LNB 9 used in multiple-beam antenna 8 must separate the received radio waves from satellites 10, 11 into mutually orthogonal horizontally and vertically polarized waves, so that each polarized wave can be transferred and supplied to a circuit portion on the board with a small amount of loss.
However, as shown in FIG. 9, waveguides 31, 32 corresponding to satellites 10, 11 are integrated by the substrate. Thus, as described with reference to FIG. 7, it is difficult to adjust polarization displacement by separately rotating each of circular waveguides 31, 32.
Therefore, a main object of the present invention is to provide a multiple-beam antenna capable of receiving radio waves from a plurality of satellites by one down converter and readily adjusting polarization displacement at a receiving location.
In short, the present invention is a multiple-beam antenna receiving radio waves from a plurality of satellites by one down converter mounted on a parabolic reflector and switching the input signals by a signal selected by a tuner for output. The down converter includes a plurality of waveguides receiving at its opening the radio waves from the plurality of satellites and converting them to linearly polarized waves, and a feeding portion inserted to each waveguide and having its one end bent to have a prescribed angle for adjusting the polarization displacement.
Therefore, according to the present invention, the polarization displacement inherent to a locational difference can be adjusted without any decrease in performance, so that a multiple-beam antenna is manufactured at a low cost. In addition, by changing an angle of one end of the feeding portion, a polarization angle can be adjusted for each location, thereby facilitating application to many types of apparatuses.
In a more preferred embodiment of the present invention, the waveguide is mounted on the board, and the other end of the feeding portion is mounted on the substrate.
Further, in a more preferred embodiment of the present invention, each satellite has a linearly polarized wave, and the feeding portion includes feeding portions respectively for horizontally and vertically polarized waves.
The waveguide includes a vertical hole formed for insertion of the feeding portion for vertically polarized wave, and a horizontal hole formed for insertion of the feeding portion for horizontally polarized wave. The end of the feeding portion for vertically polarized wave, which is to be inserted to the vertical hole of the waveguide, is angled with respect to the vertical direction for adjustment. The end of the feeding portion for horizontally polarized wave, which is to be inserted to the horizontal hole of the waveguide, is angled with respect to the horizontal direction for adjustment. The horizontal and vertical holes formed in each waveguide are arranged to form about 90xc2x0.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.